The present invention relates to a travel controller for an industrial vehicle including an engine, generator motor arranged coaxially with an engine, and a travel motor.
As one example of a prior art industrial vehicle, Japanese Laid-Open Patent Publication No. 2005-298163 describes a hybrid cargo handling industrial vehicle including an engine, a generator motor, a cargo handling pump, a travel motor, a generator motor, and a battery. The battery supplies the generator motor and travel motor with drive power. The engine, generator motor, and cargo handling pump are arranged coaxially with one another.
Japanese Laid-Open Patent Publication No. 2004-357459 describes a hybrid automobile. In this hybrid automobile, when a target torque of the travel motor is not within a tolerable torque range, the target torque is set so that the power output from the battery remains within a limited range.
In industrial vehicles such as a forklift, the vehicle speed is normally determined by the operation amount of an accelerator (e.g., depression amount of accelerator pedal). In this case, the desired vehicle speed may be obtained without having to adjust the accelerator operation amount in accordance with the load on the vehicle that increases and decreases depending on the handled cargo. In such an industrial vehicle, the acceleration, deceleration, and speed of the rotation produced by the travel motor are controlled to obtain the desired vehicle speed. When there is a difference in the power of the travel motor and the power of the generator motor, power corresponding to the difference is charged to or discharged from the battery. When the vehicle is accelerated, the power of the travel motor rapidly changes. Thus, the power of the generator motor cannot follow the power of the travel motor. Such response lag in the engine-power generator system results in the discharge of a large amount of power from the battery. The power discharged from the battery is controlled so as not to exceed a limit value, which varies in accordance with the state of the battery. However, the acceleration performance of the vehicle would be adversely affected when over-restricting acceleration so as not to exceed the limit value. Thus, it is desirable that the power discharged from the battery be prevented from exceeding the limit value without over-restricting acceleration. However, Japanese Laid-Open Patent Publication No. 2004-357459 does not address such concern.